Electrostatic discharge (ESD) is a continuing problem in the design, manufacture, and utilization of integrated circuits. A major source of ESD exposure to integrated circuits is from the human body, described by the Human Body Model. In this situation, a packaged integrated circuit acquires a charge when it is touched by a human who is electrostatically charged (e.g. from walking across a carpet). A charge of about 0.4 uC may be induced on a body capacitance of 100 pF, for example, leading to an electrostatic potential of 4 kV or more and discharge peak currents of several amperes to the integrated circuit for longer than 100 ns. A second source of ESD exposure is from charged metallic objects, described by the Machine Model, which is characterized by a greater capacitance, lower internal resistance and transients that have significantly higher peak current levels than a Human Body Model ESD source. A third source of ESD exposure is due to the discharge of stored charge on the integrated circuit itself, described by the Charged Device Model, in which the stored charge is discharged to ground with rise times of less than 500 ps. For all three sources of ESD exposure, both positive and negative polarity discharges may occur.
ESD events are a major cause of failure in integrated circuits. ESD events may occur during wafer sawing and packaging of integrated circuits, and during handling of packaged integrated circuits such as when integrated circuits are being inserted into printed circuit boards by plugging them into sockets, or by soldering, or flip chip assembly. ESD events may cause an integrated circuit to fail outright or may degrade the integrated circuit causing an early failure of the electronic assembly during use. Maintaining control of ESD events in an integrated circuit manufacturing line can be difficult and costly.